THE EFFECT OF SHORT-TERM TEMPERATURE-CHANGES ON THE MECHANICAL-PROPERTIES OF RECTANGULAR NICKEL-TITANIUM ARCHWIRES TESTED IN TORSION

Due to their exceptional temperature sensitivity, superelastic nickel titanium wires may be affected by temperature changes associated with ingestion of cold or hot food. It has been assumed that the alteration s in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of these temperat ure changes on the torsional stiffness of nickel titanium alloys. Eigh t rectangular superelastic wires were activated to 20 degrees, in long itudinal torsion at body temperature and subjected to cold (10 degrees C) or hot (80 degrees C) water with the strain held constant. The tor sional stiffness of some wires was strongly affected. The effect of ho t water disappeared quickly, but the wires remained at a level of redu ced torsional stiffness (up to 85% less than baseline) after short app lications of cold water. The most thermodynamic archwires showed incre mental reductions in torsional stiffness when cold water was repeatedl y applied. Furthermore, the torsional stiffness remained low (up to 50 % less than baseline) and showed no tendency to increase even after 2 hours of postexposure restitution. It is conceivable that some wires m ay provide inadequate forces for tooth movement after ingestion of col d liquids.